1. Field of the Invention
The present invention relates to a gas blowing plug used for blowing gas to agitate molten metal in a ladle, electric furnace, converter, degassing apparatus, and the like.
2. Description of Related Art
Conventionally, in order to promote refining reaction of molten metal, especially molten steel contained in a ladle, gas blowing is often performed. As means for this purpose, a gas blowing plug is used. FIG. 8 shows a construction of a conventional plug. A well brick 4 is disposed among bottom bricks 5 disposed on the upper side of a permanent lining 6 at the bottom of a ladle. A porous plug 2 contained in a metal case 3 is inserted from the lower side of iron shell 7 of the ladle, is supported by a holding brick 8, which is fixed by a holding plug 10. Blowing gas is supplied through a gas pipe 12, and is blown into molten metal in the ladle through the porous plug 2.
The conventional plug is made of a highly permeable refractory material, and blows Ar or N2 gas to cause nonmetallic inclusion to float up or to make the temperature uniform. As the refractory material, alumina materials, magnesia materials, zircon materials, or the like are used. The permeability is approximately in the range of 0.5 to 8 cm3−cm/cm2−s−cmH2O.
However, since the permeability must be ensured to blow a large amount of gas, it is necessary to make the material have a low density, so that the life of plug is impaired. To increase the life, the material of brick must be made dense, therefore the permeability must be decreased. Hence, it is difficult to manufacture a desirable porous plug.
To solve this problem, for example, Unexamined Japanese Patent Publication No. 11-117014 has disclosed a method in which a hot-melt sheet is formed in a spiral form, and is embedded in a refractory material and fired to make a dense plug after melting the sheet with a spiral slit inside. However, after the plug is once used, molten metal intrudes in a spiral-form slit and solidifies, so that it is sometimes difficult to blow gas into the molten metal for the next turn.
In such a case, it is normally necessary to increase the gas pressure to blow off the clogged portion. Therefore, the plug is consumed by about 5 to 20 mm for each blowing-off operation, so that the life of porous plug is decreased. When the molten metal intrudes into the slit deeply, it is sometimes difficult to blow off this portion, and in some cases, gas cannot be blown.